1. Field of the Invention
This invention relates to a battery pack having one or more battery cells enclosed therein. More particularly, it relates to a battery pack in which, on occurrence of liquid leakage in an internal battery cell, such liquid leakage is detected to prohibit the progression of malfunctions caused by such liquid leakage.
2. Description of Related Art
The battery pack, used as a driving power source for a portable electrical equipment, such as a personal computer, portable telephone or a video camera, referred to below simply as a main equipment, includes one or more battery cells and a control circuit, in its inside, these battery cells and the control circuit being interconnected by a complex interconnection.
In these battery packs, leakage of the electrolyte solution, sealed in the battery cell, is likely to occur if a shock is applied from outside to the battery pack due to descent or collision, if the exterior of the battery cell is rusted due to moisture intruded into the inside of the battery pack, or if the junction of the exterior in the vicinity of the positive electrode of the battery cell is deteriorated or punched. If such leakage of the electrolyte solution occurs in one of the battery cells in the battery pack, the electrolyte solution flows into and is spread in the inside of the battery pack to become attached to the interconnection or to a substrate of the control circuit. In the battery pack, the electrolyte solution tends to become attached to the interconnection or to a substrate of the control circuit and, after lapse of a certain time interval, metals such as copper, iron, aluminum or nickel of the interconnection or the substrate are dissolved into the electrolyte solution. In such case, the resistance of the portion to which the electrolyte solution has attached is lowered to form a new electrically conductive line of a certain resistance value. The resistance of the portions to which the electrolyte solution has attached may, for example, be on the order of 1 to 10. There are occasions where the electrically conductive line produced by leakage of the electrolyte solution is connected to both the positive and negative electrodes.
If the above-mentioned electrically conductive line has interconnected the positive and negative electrodes of the battery cell, the voltage of the battery cell is applied to the electrically conductive line so that the current flows therein to evolve heat to raise the cell temperature. For example, if the voltage of the battery cell is 4V and the resistance of the electrically conductive is 1 xcexa9, the current of 1 A flows in the electrically conductive line to evolve the heat of 4W. If, in the battery pack, the temperature of the electrically conductive line is raised gradually to reach 200 C or higher, accidents due to leakage of the electrolyte solution, such as fuming or firing, occur in the electrically conductive line.
Moreover, the heat of the electrically conductive line is transmitted to the battery cell arranged in its vicinity, such that the risk of fuming or firing occurs even in the battery cell the terminals of which are not interconnected by electrically conductive line. For example, if the heat evolved in the electrically conductive line is transmitted such that the temperature in the battery cell exceeds 130 C, the synthetic resin separator isolating the positive and negative electrodes from each other in the battery cell is dissolved to short the positive and negative electrodes to cause internal shorting to evolve heat and conseqent fuming or firing thus leading to accidents ascribable to leakage.
With the conventional battery pack, there are lacking sufficient countermeasures against occurrence of accidents ascribable to the above-described leakage of electrolyte solutions. Thus, in a certain conventional battery pack, insulating paper sheets capable of absorbing the electrolyte solution are placed about the battery cell to absorb the electrolyte solution to prevent an electrically conductive line from being formed on occurrence of leakage. In another conventional battery pack, metallic portions of the interconnection or the substrate are coated with an adhesive or a synthetic resin to prevent the metal from being dissolved in the electrolyte solution to prevent an electrically conductive line from being formed on occurrence of leakage.
However, if the insulating paper sheet is used, it is difficult to absorb the leaked electrolyte solution completely. On the other hand, if the metal portions are coated with e.g., an adhesive, such a phenomenon occurs in which the adhesive is first dissolved in the electrolyte solution before the metal portions are dissolved.
In addition, if, in the interior of the battery pack, leakage of the electrolyte solution has occurred, a user can hardly recognize the unusual occurrence, such that there is a risk of charging/discharging being repeated as the leaked state is not remedied. If the charging/discharging is repeated after the occurrence of the leakage of the electrolyte solution, the battery pack tends to fall into disorder, that is the leakage of the electrolyte solution and the dissolution of metal are allowed to progress, so that a dangerous state is apt to be produced.
It is therefore an object of the present invention to provide a battery pack in which, if leakage of the electrolyte solution occurs in the battery pack, the progress of the trouble of the battery cell or the battery pack due to the leakage of the electrolyte solution is prohibited to prevent occurrence of accidents.
In accordance with the present invention, there is provided a battery pack including a battery cell, leakage detection means for detecting the leakage of an electrolyte solution of the battery cell, current breaking means for electrically interrupting the current line between the battery cell and external terminals on occurrence of leakage of the electrolyte solution in the battery cell and discharging means having the function of self-discharging the battery cell.
In the above-described battery pack according to the present invention, if leakage occurs in an internal battery cell, it is detected by leakage detection means, and the current line between the battery cell and the external terminals is electrically interrupted by the current breaking means, so that the battery cell is self-discharged by discharging means until the voltage of the battery cell is reduced to zero. That is, should leakage occur, the electronic energy in the battery pack ultimately becomes equal to zero. So, in the present battery pack, charging/discharging is disabled on occurrence of leakage of the electrolyte solution to stop the progress of the malfunctions ascribable to such leakage to prevent accidents, such as heating, fuming or ignition from occurrence.
That is, in the battery pack according to the present invention, there is provided a function of disconnecting the connection line between the external tenminals and the battery cell on detection of leakage of the electrolyte solution, so that the battery pack in the unusual state is necessarily unusable to prevent the accident due to the leakage from progressing to prevent unusual heating and accidents of ignition or fuming ascribable to such heating.